Can you first fix for A/C just in case it's needed in future?

[cbk]

I'm about to start the first fix for plumbing and electrics for new build that is as close to Passiv Haus as I could get it and spent a lot of time trying to design out problems from solar gain - Brise Soleil features included in design etc..  Also spent a lot of time thinking about heating (ASHP) and wiring and tried to future proof things as much as possible so will run miles of cat6 cable just in case.  But this latest spell of hot weather has made me realise that overheating could still be a problem and I've not really considered options for active cooling.  A/C would be the best option and could be run for free from Solar PV.  So, I'm wondering if it is possible to put in some 'standard' A/C pipework for the bedrooms just in case this becomes an issue.  I was thinking of a standard split A/C system with a single external unit and 4 internal wall mounted units.  Would I need to get a design done to size pipes correctly or are there standard sizes (ideally pre-insulated pipework) that I could put in as a first fix item ready to conect up later if overheating was a problem.

 

Any advice, ideas or suggestions much appericiated.

[JohnMo]

Could you just install fan coil units in bedrooms, could then use for heat or cool, direct from the ASHP.  Or if you have UFH use that.

[Marvin]

2 hours ago, cbk said:

Any advice, ideas or suggestions much appericiated.

Hi @cbk

 

Our bungalow can overheat when the outside temperature is over about 11C.

 

We have fairly good AIM and APE (Airtightness, Insulation, MVHR, and ASHP, PV and EV)  AIM work well together as a set as do APE.

 

What we have found so far:

 

When using ASHP for cooling:

Radiators get condensation when the incoming water is below about 18C in a hot room. Because both valves are at the bottom of the radiarors the cold water ran along the bottom leaving the top warm.

 

The buffer tank needed to be extra insulated to avoid condensation.

 

Condensation dripped off the spinal end of the gate valve when not insulated.

 

In fact everything had to be super insulated when running at 10C in 25C air.

 

I understand that UFH cannot be run much below 18C due to condensation. Some one will clarify as we do not have it.

 

We also have MVHR in the bungalow and the loft gets over 40C at present. We have two main inlet pipes ( air into the rooms) from the MVHR box with a water coil in each, which then split so the air feeds all the required rooms. The coils are fed cold (when required hot) water from the ASHP via the buffer. From these we achieve about 19C air when 28 outside with 10C water when circulating the internal air temp as much as possible.

 

We are trying to install fans to the loft which work when the temperature is over 25 in the loft and expel the air out the building at about ridge height.

The bungalow ridge runs north/south leaving gables (and almost all the widows) east and west which have serious solar gain.

 

We have also purchased a 1kw air conditioner a few days ago which we duct to make the heated air go out of a window and I aim to duct the cooler air in from under the suspended floor eventually. (To avoid upsetting the MVHR).

 

As @JohnMo says you could use fan coil units but the set up will need to include the management of condensation water. (As we have in the loft).

 

Good luck.

 

M

[Russell griffiths]

Can you fit back to back aircon, so no ductwork needed. 

[Thorfun]

Our AC supplier offered us a first fix price as well as second fix internally without external unit price and a price for it all done. Gave us the flexibility depending on remaining funds. 

[cbk]

Thanks for the feedback guys.  I've read mixed reviews for the effectiveness of the FCU type units run form the ASHP and maybe not efective enough if there is an overheating problem.  As I'm at the first fix stage and dont yet know if I have a problem or not, I'm just trying to cover the optioins and install something suitable just in case.  My experience of ASHP installers is they have very little experience of using the cooling features and generally say it cant be done.  So maybe as @Thorfun  suggested the best option is to get a full A/C design now and request a split quote for first and second fix.  I could then remove UFH for first floor bedrooms and use the A/C for winter top up as well as summer cooling.

 

 

Edited July 17, 2022 by cbk

[JohnMo]

Just make sure you have good cross ventilation.  Keep doors and windows closed until your internal temp is the same as outside, then open everything up to get cross ventilation.  Purge the heat out.  In the morning, if it's cooler outside than inside open everything up, as the outside temps increase, close everything in again, repeat...

 

Have internal or external blinds on all windows that can get sun on them, close these as soon as the sun starts to come into the room.

 

 

[Ferdinand]

Depending on the heat soak balance an extent of high temps, cross-ventilation may ot be enough. My house starts to struggle on just cross-ventilation after two nights above say 20C between hot days.

 

I am just playing with a portable aircon / heat pump unit in this thread. To turn it from an air con to a heat pump you essentially plug it in the other way round.

 

It's currently running via an upper window, and I need to make a sealing plate. The recommendation is to run it through a wall outlet.

 

The says not to use to heat beneath ambient of 7C an dideally to get to 10C using something else, and the minimum cooling temp is 16C.

 

I'll be using it as a sort of trial this summer and next winter to explore how heating and cooling works in my house, with a view to eventually maybe swapping out my gas boiler, or limitng it to hot water only. I have lots of EW facing solar (8 KWp and 2 kWp), which should make 2-3 hours in the morning to set the place up for the day free.

 

 

Insulated 150mm air duct seems to be about £3 per metre if you buy more than say 10m of it. eg not a recommendation.

 

https://easyhvac.co.uk/index.php?id_product=13&controller=product

[Thorfun]

2 hours ago, cbk said:

I could then remove UFH for first floor bedrooms and use the A/C for winter top up as well as summer cooling.

This is exactly what we’re doing. 👍

[Ferdinand]

Incidentally, I have ordered *this* insulated 150mm duct, as it is more robust than those with an aluminium outside, and does not use fibreglass insulation.

 

https://www.amazon.co.uk/gp/product/B07HN37Q2M

[LA3222]

3 hours ago, cbk said:

Thanks for the feedback guys.  I've read mixed reviews for the effectiveness of the FCU type units run form the ASHP and maybe not efective enough if there is an overheating problem.  As I'm at the first fix stage and dont yet know if I have a problem or not, I'm just trying to cover the optioins and install something suitable just in case.  My experience of ASHP installers is they have very little experience of using the cooling features and generally say it cant be done.  So maybe as @Thorfun  suggested the best option is to get a full A/C design now and request a split quote for first and second fix.  I could then remove UFH for first floor bedrooms and use the A/C for winter top up as well as summer cooling.

 

 

I think that getting rid of first floor UFH would be a mistake. Folks are always harping on about not needing it as there is no heating requirement for a well insulated house.

 

Time and again I bang the drum for the cooling aspect. With first floor UFH you are doubling the surface area which you can cool with.

 

Any installer that says you can't run an ASHP like that is talking crap. End of.

 

My floor area is approx 140m2, double it and I have 280m2 of UFH pipes available to me. I run the ASHP in cooling node from around 9am to 6pm only on days where it is around 23 degrees and above outside. My house is not hot. It works.

 

I thought it was quite cool.today given it was supposed to be hottest day of the year, went outside around 3pm to fix kids bike tyre - bloody boiling outside. When I went back in, nice and comfortably cool.

 

My ASHP cools to 12 degrees, by time it hits the manifold it goes around house at about 15 degrees. Slight condensation on a few pipes in plant room, nothing anywhere else.

 

Job. Done.

[crispy_wafer]

Well done @LA3222 -  job well done, It seems though Installers arent keen on ASHP cooling, if done right - no problems, if wrong, then condensation risk, and mould.  A lot that I've spoken to, just aren't keen to have their business names put to a risk that may or may not happen.

 

For what it's worth to the OP, I'm putting aircon in and will put shading in place too.  The Daikin (others are available too) Heatpump Split units are pretty nice looking if wall mounting, or slim ducted units hidden in voids with diffusers located in the ceilings, or in bulkheads above doors, all accessible for future maintenance of course.  I'm planning on 2 multi split systems, one for upstairs and one for down.  I will use them for space heating this winter to see how we get on with it.  They don't need to be jet turbines blowing force 9 gales in your faces.  If it works, then I'll not bother with the ASHP, or will wait for a few years till supply and install prices come down to the same as a gas boiler.  The GF UFH gear will be going in regardless, as will plumbing for FF Rads. 

 

For the cost of the AIrcon stuff at first fix, I'm going it.  It may be a folly, but sod it, I'm doing it anyway.

 

 

[LA3222]

1 minute ago, crispy_wafer said:

Well done @LA3222 -  job well done, It seems though Installers arent keen on ASHP cooling, if done right - no problems, if wrong, then condensation risk, and mould.  A lot that I've spoken to, just aren't keen to have their business names put to a risk that may or may not happen.

I havent done anything that many others on here hadn't already done. The only slight difference in my setup is that I advocate for FF UFH in order to increase the ability to cool the house.

 

Other than exposed pipes in the plant room (nothing is insulated yet), I cant see condensation/mould being an issue.

 

If you were to use radiators then that would pose a problem. UFH pipes in a slab, nah.

[markocosic]

First fix boxes make slapping the wall units on later easier:

 

 

https://www.vecamco.com/prodotto/dry-safe-box/?lang=en 

 

etc

 

then it's just a case of burying your drain line, the copper lines to your final outdoor unit location, electric cables between the two etc

 

Given that the AC unit is perhaps £750-£1500 worth of the install cost you might as well fit it at the outset imo.

 

 

Another option is a ceiling cassette at the top of the stairs on the first floor. That'll cool upstairs rooms during daytime if does are left open; and coolth will fall down that stays to take the edge off downstairs too.

 

 

Fairly out of the way and can hardly be installed after the event with poor and cable through attic and down an outside wall to the outdoor unit. They include condensate pumps with a lift of 750+ mm so that gives you lots of room in the attic to run the condensate to a soil stack boss etc.

 

The catch? You'll need >600 mm centres on your joists. I'd suggest 750 spacing where this goes. Some are close to fitting (e.g 580 mm) but that leaves little for building an insulated airtight box on top.